Fine-needle aspiration biopsy of the thyroid: atypical cytopathological features.

OBJECTIVES To evaluate the positive predictive value of a thyroid nodule being malignant when categorized as atypical, and to determine the prognostic implications of specific cytopathological features. DESIGN Retrospective review of consecutive patients undergoing thyroid surgery following fine-needle aspiration biopsy (FNAB) of thyroid nodules. SETTING Academic teaching hospital in Toronto, Ontario. PATIENTS A total of 111 consecutive patients with atypical findings from an FNAB who underwent thyroid surgery from January 2000 to November 2005. RESULTS Of 111 patients included in this study, 62 (56%) were diagnosed with a thyroid malignancy on final histopathological examination. The remaining 49 patients (44%) had benign disease. When comparing patients with a postoperative diagnosis of malignancy vs those with benign disease, micronucleoli (71% vs 49%; P = .01), nuclear grooves (50% vs 31%; P = .03), and powdery chromatin (37% vs 16%; P = .01) were more frequently observed in the group with cancer. The probability of malignancy was 83% if all 3 of these features were present; 32% if none of these features was present (P = .001). CONCLUSIONS At our institution, when findings from a thyroid nodule FNAB sample were categorized as atypical, the positive predictive value of the nodule being malignant was 56%. In this series of patients, the presence of micronucleoli, nuclear grooves, and powdery chromatin increased the likelihood that an atypical specimen was representative of malignant disease. These features may help guide treatment of patients with atypical findings from a thyroid nodule FNAB sample.